Generally, washing machines are electric home appliances that are widely used at home. The washing machines are machines that remove contaminants from laundry, such as clothes or bedclothes, using emulsification of detergent, friction of washing water motion generated by washing machine drum rotation, and impact applied to the laundry.
Washing machines are classified into a pulsator type washing machine, a drum of which is mounted in a vertical direction, and a drum type washing machine, the drum of which is mounted in a horizontal direction.
Normally, a washing operation is a course of supplying detergent and washing water to laundry to be washed such that contaminants can be removed from the laundry by a chemical action of the detergent contained in the washing water and a physical action of a drum.
A rinsing operation is a course of supplying washing water containing no detergent therein such that the detergent and contaminants can be rinsed out of the laundry, and a spin-drying operation is a course of rotating a washing tub at high speed, after the rinsing operation is completed, such that moisture can be removed from the laundry.
In recent years, as the awareness level of drum type washing machines that can wash laundry with reduced damage to the laundry has increased, and therefore, the use of the drum type washing machines has greatly increased, washing-and-drying machines, which are capable of washing and drying laundry, thereby improving the convenience of use, have been placed on the market.
The conventional washing machines consume a relatively large amount of washing water while a washing operation is carried out. For this reason, attempts to minimize the amount of washing water used to wash laundry have been made in recent years.
As a result of such attempts, there has been developed a washing machine having a steam generation unit mounted therein. The steam generation unit serves to supply high-temperature steam into a drum of the washing machine such that a washing operation can be carried out with high efficiency using a relatively small amount of washing water.
On the other hand, when various mixtures, such as contaminants separated from the laundry or residua of detergent, are accumulated or attached to the inner/outer wall of the drum and inside the tub, laundry to be washed is contaminated during the washing operation, and therefore, the washing efficiency is lowered.
Furthermore, when the tub assembly (which includes the drum and the tub) is contaminated, a bad smell is given off from the interior of the washing water by bacilli, such as mold, growing on the contaminants.
In the conventional art, in order to solve the tub assembly contamination, only washing water is supplied into the drum while laundry to be washed is not placed in the drum, and then the drum is submerged in the washing water for a long period of time while detergent is dissolved in the washing water to wash the tub assembly.